This invention relates to the upgrading of heavy crude feedstocks of high molecular weight. Such crudes are characterized by high metal, sulfur, Conradson Carbon, and asphaltene content. This invention will thus be useful in geographic areas, such as the Orinoco Oil Belt, the Tar Sands of Athabasca, and Boscan, etc., where this type of crude is common. Typically, crudes from these areas have a metal content of 400-1400 ppm of vanadium (V) plus nickel (Ni), a sulfur content of 3-5%, a high content of both Conradson Carbon and asphaltene, and a small (30-40% v/v) distillate fraction. The high viscosity and density of these crudes make them difficult to transport. In addition, their processing in conventional refineries is not possible.
Numerous publications describe methods of producing distillates and removal of asphaltenes and/or metals through the use of one or several conversion stages. For example, Venezuelan Pat. No. 2144-77 discloses a catalytic hydrocracking or cracking process using conventional catalysts followed by catalytic hydrotreatment and deasphalting operation as supplemental stages. In U.S. Pat. No. 3,576,737 a vacuum residue is treated with a vanadium containing catalyst, having pores larger than 300 .ANG. in diameter, at a temperature of 600.degree. to 900.degree. F. and a hydrogen pressure of 100 to 3000 psig. Metal removal using a catalyst consisting of Group VIB or Group VIII metals, supported on alumina, is taught by U.S. Pat. No. 3,227,645. Other descriptions of the prior art are contained in U.S. Pat. No. 2,689,825, which discloses the use of catalysts removed from the catalytic cracking zone and their employment as metal contaminant-absorbing elements, and U.S. Pat. No. 3,876,530, which describes several stages of treatment with Group VIB and Group VIII catalysts on neutral alumina. This patent in turn mentions other catalysts of the CoMo and NiMo type on different carriers.
The use of synthetic supports such as alumina, silica-alumina, or zeolites, either alone or impregnated with active metals, has limitations when employed on a crude such as those contemplated by this invention. For example, black oils, which are the preferred feedstock for the present invention, have a high concentration of metal contaminants (typically over 400 ppm of V+Ni) in the form of dissolved organo-metallic compounds. These compounds decompose under typical processing conditions and deposit on the surface of the catalyst, decreasing catalyst activity. This catalyst degradation increases the aost of the upgrading process.
A synthetic suspended catalyst for use in hydrogenolysis of heavy crudes is described in U.S. Pat. No. 2,715,603. Severe temperature and pressure conditions are employed. The product, after fractionation and deasphalting, is converted to distillates. U.S. Pat. No. 4,176,048 discloses a first hydrotreating stage, followed by a deasphalting step and an intense hydrocracking of the deasphalted oils. The catalysts employed are Group VIB and Group VIII metals, supported on a refractory material of large pore diameters.
U.S. Pat. No. 2,771,401 describes the use of a synthetic cracking catalyst for demetallization purposes. Similarly, U.S. Pat. No. 3,893,913 discloses the use of a naturally available material, such as bauxite, impregnated with a Group VIB or Group VIII metal.
In the prior art, when inexpensive carriers such as bauxite have been employed in the hydrotreating or hydrocracking step, the degree of demetallization of the crude has been limited despite severe processing conditions of 2000 psi or more. Accordingly, the quality of the unconverted material (i.e., that boiling over 950.degree. F.) is low. It is also well known that these bottoms are unstable and carbonaceous deposits tend to precipitate therein when they are mixed with lighter fractions, as is common in the industry.
U.S. Pat. Nos. 2,975,121 and 2,910,434 disclose non-catalytic demetallization processes consisting of hydrogenation of black oil, either in a homogenous phase or employing an inert solid, followed by solvent deasphalting. This procedure gives rise to considerable gas and coke production, which diminishes the liquid yield of the upgraded product.
U.S. Pat. No. 4,298,460 discloses the use of iron catalysts, primarily for capturing sulfur in its reduced state (valence less than three). However, such reduced catalysts incur larger hydrogen consumptions and increased capital costs because a reduction stage would be required before the catalyst enters the hydroconversion reactor. This does not produce any known beneficial effect with respect to the hydroconversion process. Furthermore, presulfided iron catalysts which are effective in hydroconversion are ineffective for the purposes of U.S. Pat. No. 4,298,460. Because of these limitations of the distinctly different processing routes, U.S. Pat. No. 4,298,460 teaches that at least 30% iron is required, whereas it has now been discovered in this invention described below that this high iron content is unnecessary for hydroconversion processes. These distinctions are further emphasized by U.S. Pat. No. 4,298,460 which is directed to a fluid catalytic cracking process giving rise to high coke production and low liquid yield of the upgraded product. As is well known, a high liquid yield, in % by weight in the upgrading process, is an essential requirement for syncrude projects to be economical. It has now been advantageously found in this invention herein that a 92% by weight yield of high quality upgraded crude is obtained in contrast to U.S. Pat. No. 4 298,460. Furthermore, as demonstrated herein this high liquid yield is all distillable C.sub.5.sup.+ meaning that 100% conversion of the vacuum bottoms (950.degree. F.+) of the heavy crude is achieved through the present invention. Also, it is known in the art that a catalyst composition effective in fluid catalytic cracking is ineffective in hydroconversion (see Charles L. Thomas, Catalytic Processes and Proven Catalysts, pages 29-32 and page 175). Such catalytic cracking catalysts, when employed in hydroconversion have historically produced unsatisfactorily high coke yields.
U.S. Pat. No. 3,859,199 includes a deasphalting section after a catalytic desulphurization section, in which expensive synthetic catalysts (cobalt/molybdenum on alumina is recommended) are employed. Feed to the catalytic desulphurization section is an asphaltenic feedstock of which no reference is made to its metal content. Where a feedstock high in metal content, e.g., greater than 200 ppm metals is employed, this high level of metals would quickly poison the catalysts in the catalytic desulphurization section, as proposed in U.S. Pat. No. 3,859,199, thereby incurring a high operating cost because of large consumption of expensive catalysts.
The above processes all have limitations with respect to the extent to which heavy feedstocks are upgraded or with respect to the economic attractiveness of the process due to high catalyst cost, low quality in some fractions of the product, or excessive capital costs due to the need for severe processing conditions.